On the Estimation of Join Result Sizes
On the Estimation of Join Result Sizes
复制标题
关于连接结果大小的估计
DOI：
10.1007/3-540-57818-8_58
复制
发表时间：
1994
影响因子：
--
通讯作者：
K. Schiefer
中科院分区：
文献类型：
--
作者：
A. Swami;K. Schiefer
联合结果尺寸的良好估计对于关系数据库管理系统中的查询优化至关重要。我们解决了逐步获得联合结果大小的准确且一致估计的问题。我们已经发明了一个新规则，用于选择加入选择性以估计联接结果大小。该规则是一种称为算法ELS（等效性和最大选择性）的新统一算法的一部分。在计算任何结果尺寸之前，确定了与联接列的等价类别。该算法还考虑了局部谓词对表和柱红外的影响。这些计算允许计算每个合格的联接谓词的正确选择性值。我们表明，该算法是正确的，并且比当前估计算法提供了更好的估计。
Good estimates of join result sizes are critical for query optimization in relational database management systems. We address the problem of incrementally obtaining accurate and consistent estimates of join result sizes. We have invented a new rule for choosing join selectivities for estimating join result sizes. The rule is part of a new unified algorithm called Algorithm ELS (Equivalence and Largest Selectivity). Prior to computing any result sizes, equivalence classes are determined for the join columns. The algorithm also takes into account the effect of local predicates on table and column cardinalities. These computations allow the correct selectivity values for each eligible join predicate to be computed. We show that the algorithm is correct and gives better estimates than current estimation algorithms.